An antenna tuning can be achieved for example by connecting lumped elements (capacitors, inductors) to an antenna structure or by manually changing antenna structural dimensions, such as the electrical length of the antenna element or a distance to a ground.
Moreover, it is possible to use different materials, which have a certain magnetic permeability or dielectric constant, embedded in between a ground plane and an antenna element. Also, it is possible to switch between different matching circuit states for varying an antenna matching band.
Several articles in the open scientific literature describe tuning methods for microstrip antenna elements. For example reference [1], wherein especially included papers [P8] and [P9], and the references therein. Proposals have been made, for example, to connect a tunable reactance (e.g. tunable capacitor) between an antenna element and a ground plate, to utilise switchable slots, or to utilise a switchable matching circuit for tuning a matching band location. In addition, in reference [2] is presented an overview of RF-MEMS enabled tunable antennas, in reference [3], which corresponds to preceding paper [P9], is presented a transmission line tuning, and in reference [4], for one, is disclosed a movable dielectric material together with a tunable planar inverted F antenna (PIFA).
Since the trend in a communications antenna design is towards smaller physical dimensions and as small as possible number of antennas, the antenna tuning plays an important role. The efficient re-use of the mobile phone antennas through a low cost tuning would be highly desirable, particularly if very fast tuning would be possible.